Purification of ammonia syngas

Claim 1

In the separation of a multicomponent feed gas mixture for recovery therefrom of contained major components consisting of hydrogen and nitrogen freed of carbon dioxide and further substantially freed of minor components from the group consisting of methane and carbon monoxide, the method which comprises in an adiabatic adsorption pressure swing cycle the steps of: (a) passing such multicomponent gas mixture at initial super-atmospheric pressure in selected flow direction through a first sorbent bed (A) selective for preferential retention of carbon dioxide and then passing the effluent from said first bed through a second sorbent bed (B) selective for retention of said minor components while discharging from said second sorbent bed unadsorbed hydrogen and nitrogen, said passing of said multicomponent gas mixture being continued for a controlled time period short of breakthrough of carbon dioxide from said first sorbent bed, while retaining in said second bed substantially all of sorbed methane and any carbon monoxide present in said mixture; (b) thereafter discontinuing gas flow communication between said first and second sorbent beds, and (i) rinsing said first bed by flowing a stream of relatively pure carbon dioxide therethrough at substantially the initial super-atmospheric pressure of step (a) for a controlled time period effective to remove most of the void and displaced gases from said first bed, and during this time period (b), (ii) lowering the pressure in said second bed to an intermediate level by withdrawal therefrom of a gas stream containing void and desorbed gases, and thereafter (iii) further depressuring said second bed to near ambient pressure followed by purging the second bed at near ambient pressure with a stream of the recovered major components: (c) after said rinsing step in (b) above reducing the pressure in said first bed to an intermediate level by desorption of gas therefrom including previously sorbed carbon dioxide and during this step (c) repressuring said second bed to an intermediate pressure level by flow thereinto of gas substantially free of carbon dioxide; (d) following step (c) above further desorbing gas from said first bed to lower the pressure therein to substantially ambient level, and thereafter (e) purging said first bed with a stream consisting essentially of said minor components, CH 4 and CO and small amounts of the major components, H 2 and N 2 purged from said second bed during step (iii) above; (f) introducing into the purged first bed a gas stream substantially free of carbon dioxide to bring said first bed to an intermediate pressure level, and thereafter (g) further repressuring said first bed to initial super-atmospheric pressure level by flowing thereinto a stream of hydrogen and nitrogen via a second bed which had already been brought to intermediate pressure level, thereby bringing both said beds to the super-atmospheric pressure of step (a) and making them ready to repeat the defined sequence of steps beginning with the reintroduction of the multicomponent feed gas mixture into said first sorbent bed.